Problem: $120$ is what percent of $300$ ?
Having a percent of something means that you get that percent out of every $100$ We can set up a proportion to find out what percent of $300$ we need to take to get $120$ $ \dfrac{{\text{percent}}}{100} = \dfrac{{\text{part}}}{{\text{whole}}}$ Which things do we know, and what are we trying to find? We are trying to find the ${\text{percent}}$ . Is $300$ the ${\text{part}}$ or the ${\text{whole}}$ The $300$ is the ${\text{whole}}$ . This means the ${\text{part}}$ is $120$ $ \dfrac{{\text{percent}}}{100} = \dfrac{{120}}{{300}}$ If we divide the denominator of the fraction on the right by $3$ , it will be the same denominator of the fraction on the left. To keep things equal, let's also divide the numerator on the right by $3$ $ \dfrac{{\text{percent}}}{100 } = \dfrac{{120 \div 3}}{{300 \div 3}}$ $ \dfrac{{\text{percent}}}{100 } = \dfrac{{40}}{{100}}$ $ {\text{percent}} = {40}$ So $120$ is $40\%$ of $300$.